1. Field of the Invention
The present invention relates to a baseplate for a disk drive suspension used in an information processing device, such as a personal computer, and a method for manufacturing the baseplate.
2. Description of the Related Art
A hard disk drive (HDD) is used in an information processing apparatus, such as a personal computer. The hard disk drive comprises a magnetic disk rotatable about a spindle, actuator arm, positioning motor, etc. The actuator arm is moved transversely relative to tracks about a pivot by the positioning motor. A suspension is mounted on the distal end portion of the actuator arm.
The suspension comprises a baseplate (or mount plate), load beam, flexure, etc. The baseplate is fixed to the actuator arm. The load beam is fixed to the baseplate directly or by means of a hinge member. The flexure is located along the load beam. A slider, which constitutes a magnetic head, is disposed on the distal end portion of the flexure. The baseplate is formed of an iron-group metal, such as austenite stainless steel (e.g., SUS304 described later). This baseplate is press-formed into a predetermined shape. An example of a suspension with a baseplate is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-31872 (Patent Document 1).
A cylindrical boss portion is formed on the baseplate of the suspension in order to fix the baseplate to the actuator arm. The boss portion is inserted into a circular mounting hole in the actuator arm and fixed to the actuator arm by fixing means. An example of a baseplate with a boss portion is disclosed in Japanese Patent No. 3563037 (Patent Document 2).
Plastic working called “ball caulking” is known as an example of the fixing means. In the ball caulking, a hard ball, such as a steel ball, is passed through the interior of the boss portion to enlarge its diameter. By the ball caulking, the outer peripheral surface of the boss portion is fixed to the inner peripheral surface of the mounting hole in the actuator arm. If the boss portion is press-formed, it may sometimes be work-hardened. In this case, the hardness of the boss portion is reduced by heat treatment before the ball caulking is performed, for example.
It is not automatic that if the hardness of the boss portion is reduced by heat-treating the baseplate as described above, then the coefficient of friction between the ball and the inner surface of the boss portion will be reduced. Therefore, a great ball insertion force may be required in some cases. If the difference between the diameter of the ball and the inside diameter of a ball insertion hole is reduced in order to facilitate the passage of the ball, the required insertion force can be reduced. In that case, however, the diameter of the boss portion cannot be sufficiently enlarged by the ball caulking, so that the strength with which the boss portion is secured to the actuator arm is insufficient.
If the difference between the ball diameter and the inside diameter of the ball insertion hole is increased, on the other hand, the passage of the ball requires too great a force (ball insertion force). Therefore, that area of the baseplate which surrounds the boss portion may be deformed, thereby adversely affecting the properties of the suspension. In order to reduce the frictional resistance produced by the passage of the ball, it is proposed to form a film of, for example, an alcohol-based lubricant on the inner surface of the boss portion. However, this method requires a process for applying the lubricant on the inner surface of the boss portion, process for removing the lubricant, etc., resulting in an undesirable increase in the number of processes.